1. Field of the Invention
The present invention generally relates to the field of orthopaedic implants. Specifically, the present invention provides a prosthetic implant to replace spinal vertebra and adjacent intervertebral discs.
2. Background
The vertebral column serves as the main structural support of the human skeleton. The vertebral column consists of a number of vertebrae separated by intervertebral discs. A vertebra approximates a cylindrical shape, with wing-like projections and a bony arch. The arches create a passageway through which the spinal cord runs. The vertebral column is held upright by fibrous bands of muscle and ligament. There are seven vertebrae in the cervical region, twelve in the thoracic region, five in the lumbar region, and five in the sacral region that are usually fused together. The integrity of the vertebral column is critical to protecting the fragile spinal cord, in addition to its duties in supporting the skeleton.
When a vertebra or intervertebral disc becomes damaged, either through trauma or disease, the spinal cord or nerve roots may be impinged, causing a great deal of pain. This pain can occur almost anywhere in a person's body, from the back or neck to the extremities. In such a case, patients often receive drug treatment in an initial attempt to relieve the pain, but if that is unsuccessful, it may be necessary to remove all or a portion of one or more vertebrae, including the anterior cylindrical body, which is the load-bearing portion of intervertebral discs. When this procedure is undertaken, it necessarily weakens the support structure of the spinal column, and the excised material must be replaced with some load-bearing material. Given the high propensity of spinal discs to degenerate in human beings, the need for an efficient and stable method of spinal fixation is tremendous.
It is possible to replace the excised vertebral bone with a bone graft. The bone graft may be an autograft, normally harvested from the patient's iliac crest, or, alternatively, may be an allograft—tissue obtained from a human donor. Once the bone graft is in place spanning the bony defect, it fuses over time with the remaining healthy vertebrae. Generally, a metal plate and screws are used to secure the bone graft to the natural vertebrae, providing support until the fusion process is complete. However, given that it generally takes between three and six months for bony fusion to occur, a more substantive prosthetic implant is often used to stabilize the spine, often in combination with bone graft that can grow out of the prosthesis and fuse with the adjacent bone over time.
A prosthetic spinal fixation device should accurately replace the height of the excised material, result in acceptable tension levels in the spine, maintain proper curvature of the spine, obtain balance through the spinal segments, and restore normal load-bearing characteristics throughout the spine.
Moreover, a prosthetic spinal fixation device should be easily adjustable to allow the surgeon to quickly select the height of the device during surgery to fit the needs of the patient. The desired height of the device will depend on the amount of bone that is removed from the patient, the size of the patient, as well as the location of the removed bone (i.e. cervical region or lumbar region). In addition, a one-size-fits-all device may reduce manufacturing costs because fewer different parts and/or models will be required to meet the needs of the marketplace.
While prosthetic corpectomy implants are known in the art, a need exists for improved implants that are more easily adjusted to achieve the necessary height to replace the excised bone during the implantation process, while also possessing the biomechanical properties necessary for long-term implantation in the human body and the immediate fixation ability to provide stability to the spinal column.